Abstract
We have investigated the properties of defects in MnO bulk and at (100) surfaces, as used in catalytic applications, using hybrid-level density functional theory (i.e., inclusion of exact exchange within the exchange-correlation evaluation) in a hybrid QM/MM embedded-cluster approach. Initially, we calculate the formation energy for bulk Mn and O vacancies, comparing charged-defect compensation with charge carriers at the Fermi Level (ϵf) and through Schottky defect formation. Oxygen vacancies were also investigated at the (100) surface, where the vacancy formation energy is very similar to the bulk. Defect levels associated with the most stable vacancies are calculated using the ΔSCF method: all are positioned mid band gap, with surface environments failing to alter strongly the overall nature of the defect relative to bulk. Chemical activity of the (100) MnO surface was considered through the adsorption of a probe CO2 molecule, which is considered the initial step in the transformation of CO2 into hydro...
Highlights
Understanding the properties and stability of material defects is key in order to maximize the impact of materials engineering
Rock salt metal oxides are ideal test systems when studying how defects alter fundamental physico-chemical behavior,[1−4] with their stability making them appealing for applications that do not involve ambient conditions, such as heterogeneous catalysis.[5−8] In particular, rock salt oxides formed from early group 2 alkaline earth metals (Mg, Ca) have been extensively studied, both with respect to their defect structure and properties[9] and with the focus on potential applications in the catalytic transformation of CO2.10,11 In these investigations, computational methods lend themselves to investigating both the viability of reaction mechanisms as well as the large compositional search space for novel materials, with systematic investigations establishing a new standard when looking for beneficial material characteristics.[12,13]
One material that plays an important role in these studies is MnO(s) [ΔHf (MnO), which is typically considered as a supporting material or a reaction promoter, rather than an active part of catalytic processes, due to its variable oxidation state;[15−19] in this highlighted work, MnO was identified as being reactive toward CO and CO2.18,19 This is perhaps unsurprising given that MnO can be prepared by thermal decomposition of MnCO3,20,21 which is done in an anaerobic environment to prevent the formation of higher oxidation state compounds
Summary
Understanding the properties and stability of material defects is key in order to maximize the impact of materials engineering. We introduce our chosen methodology, hybrid quantum- and molecular-mechanics, and we investigate the electronic and energetic properties of defects in bulk MnO, providing new insight into the bulk properties of this material. We complement these calculations with an investigation of surface atomic vacancies at the low-energy (100) surface, and we test the reactivity of CO2 over both pristine and defective MnO (100) surfaces
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
